Referring to FIG. 1, this disclosure concerns a smoking article 120, such as a cigarette, which preferably comprises a tobacco rod 122 and a filter 132 attached to one end of the tobacco rod 122 with tipping paper 132. Preferably, the tobacco rod 122 comprises a column of shredded tobacco (“cut filler”) and a wrapper 123 disposed about the column of tobacco, which wrapper 123 is constructed in accordance with teachings which follow. The tobacco rod 122 has a lightable or lit end 124 and a tipped end 130 (which in the case of non-filtered cigarettes, is referenced as the mouth end 130 of the cigarette 120). Cut filler tobacco is an industry-standard designation. Further, the tobacco rod 122 typically has a generally circular cross section, although other oval cross section and other non-circular shapes are within the scope of this disclosure. The wrapper is sealed along a longitudinal seam to form the tobacco rod 122.
The tobacco rod has a nominal length measured from the edge 131 of the tipping paper to the free end of the tobacco rod along a longitudinal axis of smoking article. By way of example, that nominal length may lie in the range of about 60 to about 100 mm.
The “wrapper” paper 123 (see FIG. 2) typically includes a “base web” 140 that may be made from flax, wood pulp, cellulose fiber, or the like, and may have a plurality of banded regions 126 applied to one or both sides. Preferably, the banded region 126 is applied to the inside of the wrapper 123 in the sense of how the wrapper 123 surrounds a column of tobacco in the tobacco rod 122.
In the manufacture of base web suited for the construction of the various embodiments of print banded paper disclosed herein, such manufacture usually will include the production of a roll of base web of several feet across (usually about 3 feet across or in transverse dimension), which is then slit into bobbins. Printing operations are preferably conducted on the rolls, but could be conducted after slitting. Preferably, the bobbins themselves will have a transverse dimension equivalent to the width needed to make tobacco rods 122 or an integral number of such widths (e.g., 1, 2, or 4 of such widths). The bobbins are adapted for use with typical cigarette making machines. The wrapper preferably has a dimension in cross-direction that takes into account the nominal circumference of the tobacco rod and an overlapping seam. As a result, when the wrapper is slit, the smoking article formed therefrom always has a longitudinal seam with an exact overlap.
For purposes of this disclosure, “longitudinal” refers to the direction along the length of a tobacco rod (e.g., along the axis 134 in FIG. 1), or along the length of a base web 140 (e.g., arrow 142 in FIG. 2) used in the preparation of wrapper that, in turn, may be used to fabricate a tobacco rod.
For purposes of this disclosure, “transverse” refers to the direction circumferentially around a tobacco rod 122 (see FIG. 1), or transversely of a base web 140 (e.g., arrow 144 in FIG. 2) used in the preparation of wrapper that, in turn, may be used to fabricate a tobacco rod.
For purposes of this disclosure, a “banded region” or “zone” is an area 126 (see FIG. 2) on an underlying base web 140 to which an add-on material has been applied. The banded region typically exhibits a two-dimensional pattern or array on the base web 140. More specifically, the pattern or array may comprise repeating units in the longitudinal direction 142 of the base web 140, repeating units in the transverse direction 144 of the base web 123, and or units which repeat in both the transverse 144 and longitudinal 142 directions of the base web 140. The regions 126 of add-on material are applied to the wrapper 123 to obtain satisfactory or improved Ignition Propensity (“IP”) characteristics and may also obtain improved Self-Extinguishment (“SE”) characteristics.
The regions 126 of add-on material are spaced along the base web 140 such that at least one region of add-on material 126 is positioned between the first and second ends 128, 130 of the tobacco rod 122 in each finished smoking article, but more preferably at least two regions of add-on material may appear on the tobacco rod 122. The region 126 of add-on material preferably extends in the circumferential direction at one or more spaced locations along the axis 134, extending around the tobacco rod 122 of the smoking article 120. While the region 126 of add-on material is depicted in this disclosure as containing discontinuities in its circumferential direction, other configurations for the add-on material are within the spirit and scope of this disclosure, including, but not limited to, configurations where the add-on material is substantially continuous.
It is noted for sake of convention that, in describing dimensions of various embodiments herein, that band or zone “width” extends in a longitudinal direction 134 (see FIG. 1) of the tobacco rod 122, whereas a dimension in the circumferential direction will be expressed as “circumferential” or “transverse” or “in cross-direction.”
Where the banded region 126 extends transversely of the base web 140 (or circumferentially around a tobacco rod), the “width” of the banded region 126 is measured in the longitudinal direction 142 from the leading edge 146 to the trailing edge 148 and is preferably lies in the range of from about 5 to about 9 mm (from the leading edge 146 to the trailing edge 148), more preferably from about 5.5 to about 7.5 mm, and even more preferably from about 6 to about 7 mm. Further, banded regions may have a 27 mm “phase” (i.e., the spacing from the leading edge 146 of one banded region 126 to the leading edge 145 of the next adjacent banded region 126). Preferably, the banded regions of add-on material reduce permeability of the wrapper to the range of from about 0 to about 12 CORESTA.
For purposes of this disclosure, “band spacing” refers to the distance between the trailing edge 148 of one banded region 126 and the leading edge 146 of an adjacent banded region 126 on the base web 140 from which a wrapper is fashioned.
As used herein, the phrase “leading edge” refers to the edge 146 (see FIG. 1) of a banded region 126 that is closest to an approaching coal during smoldering of a smoking article 120 whose wrapper 123 contains the banded region 126, while the phrase “trailing edge” refers to the edge 148 of a banded region 126 that is farthest from an approaching coal during smoldering of a smoking article 120 whose wrapper 123 contains the banded region 126.
For purposes of this disclosure, “layer” refers to a quantity of add-on material applied to a base web from which a wrapper is fabricated. Each banded region 126 may be formed by applying a “layer” 210 of an aqueous film-forming composition to the base web 140 of the wrapper to reduce the permeability of the paper in the corresponding banded region.
Where a film-forming composition is used, that “film-forming composition” preferably may include water and a high concentration of an occluding agent, e.g., 14% to about 50% by weight. The film-forming compound can include one or more occluding agents such as starch, alginate, cellulose or gum and may also include calcium carbonate as a filler. Further, the film-forming composition preferably includes an anti-wrinkling agent. Where starch is the film-forming compound, a concentration of at least about 25% may be particularly advantageous, and a concentration of about 30% is presently most preferred.
An “anti-wrinkling agent” is a material which inhibits transverse shrinkage of the base web 140 (see FIG. 2) during printing or other conversion operations. A suitable anti-wrinkling agent may be selected from the group consisting of 1,2 propylene glycol, propylene glycol, glycerin, and starch plasticizing agents.
The film-forming composition may be applied to the base web of the wrapper 140 using conversion technologies such as gravure printing, digital printing, coating or spraying using a template, or any other suitable technique.
When discussing application rates for add-on material applied using gravure printing techniques, often use values with “X” as a suffix to refer to a volumetric application rate. The table below sets out the volumetric equivalents for “X” in terms of billion cubic microns, or “BCM”:
VolumeBCM0.5X3.41.0X4.61.5X6.82.0X102.5X10.73.0X12.33.5X13.64.0X17.84.5X19.95.0X22.45.5X24.76.0X27.8
In this specification, the unit of measurement for basis weight, gram(s) per square meter, is abbreviated as “gsm”.
When the phrase “weight ratio” is used herein with respect to the starch component of a starch solution, the “weight ratio” is the ratio of the weight of the additional material compared to the weight of starch used to prepare the starch solution. Moreover, for purposes of this disclosure, references to an “X % starch solution” refer to an aqueous starch solution in which the starch weight is X % of the solution weight (e.g., weight of starch divided by the sum of starch weight and aqueous component weight).
The wrapper includes a base web which typically is permeable to air. Permeability of wrapper is typically identified in CORESTA units. A CORESTA unit measures paper permeability in terms of volumetric flow rate (i.e., cm3/sec) per unit area (i.e., cm2) per unit pressure drop (i.e., cm of water). The base web of conventional wrapper also has well-known basis weights, measured in grams per square meter, abbreviated as “gsm”. The permeability and basis weight for the base web of typical smoking article papers commonly used in the industry are set out in the table below:
Permeability, CORESTA unitsBasis Weight, gsm2425332546256026-27
For purposes of this description, the base web of a preferred wrapper has a permeability of at least about 20 CORESTA units. Most preferably, the wrapper has a permeability greater than about 30 CORESTA, such as common base webs having nominal permeabilities of about 33 and about 46 CORESTA with a basis weight of about 25 gsm. For some applications, the base web may have a permeability of greater than about 60 CORESTA, or greater than about 80 CORESTA, or even higher permeability values.
Schematic vs. Actual Depictions
Depictions of cross sections taken through a banded paper, such as FIG. 7, are believed to be useful schematic representations of a paper web having banded regions fashioned from a single application, and of the application processes by which such banded papers are fabricated. However, such schematic representations do not accurately depict the reality of the cross-section base web structures, or the reality of the cross-section of base web structures to which a layer of add-on material has been applied, or the reality of the cross-section of the layer of add-on material, in the final banded paper product.
More particularly, FIG. 4 is a mosaic of photomicrographs taken of a cross-section of a banded wrapper of the type discussed above and elsewhere in this disclosure. The photomicrographs of FIG. 4 cover an actual length of wrapper measuring about 2.1 mm in length, to which add-on material has been applied in two layers—one layer containing starch and calcium carbonate, and one layer having starch but no calcium carbonate. Match lines are applied to the different sheets of the FIG. 4 mosaic so that the relationship between different portions of FIG. 4 are readily apparent.
The individual photomicrographs of FIG. 4 enlarge the actual paper sample 2500 times. Procedurally, actual banded paper was cut into sections several millimeters long and embedded into Spurr™ epoxy. The embedded paper was then cut into 5 μm (micrometers) thick cross sections using a Leica Ultracut UCT Ultramicrotome equipped with a glass knife. The sample was mounted on a carbon adhesive disk attached to an aluminum stub, and sputter coated with 15 nm (nanometers) of Au—Pd using a Cressington 208HR Sputter Coater operating in argon. The sample was imaged in adjacent overlapping portions using an FEI XL30 Environmental Scanning Electron Microscope (ESEM) operating at 15 kV in Hi-Vac mode.
FIGS. 4A, 4B depict a portion of the base web 140 which is free of any add-on material. The base web 140 includes a multiplicity of randomly dispersed, light areas (e.g., 160) which represent calcium carbonate particles incorporated into the base web during paper formation. The base web 140 also includes a multiplicity of darker shapes 162 some of which are elongated, others of being rounded, which are cuts through fibers used in the paper making process. The base web 140 has a pair of surfaces 161, 163, that can be characterized as having random roughness at this level of magnification, and having both calcium carbonate particles and fibers randomly distributed along the surface regions. The base web 140 itself exhibits a thickness which, at best, may also be characterized as random, but having some statistically average or nominal value.
When the first portion or layer of add-on material 164 is applied (see FIG. 4C), the add-on material shows on the surface of the base web 140 due principally to the presence of chalk (or calcium carbonate) in the material. In the sample which has been magnified in FIG. 4, the second portion or layer of add-on material 166 is applied (see FIG. 4C) on the surface of the base web 140 and is positioned on the first layer 164. The second layer 166 begins at about the location 168 (FIG. 4C). While it appears that the second layer 166 is not aligned so as to start at the same location as the first layer 164, the tolerances involved in application techniques such as printing effectively do not allow the layers to be controlled within a tolerance of any less than about 0.3 mm. From the scale of magnification shown on the images of the FIG. 4 mosaic, the distance between the beginning of the first layer and the beginning of the second layer is about 0.12 mm—a distance well within the minimum tolerance noted above.
Examining the first layer as it extends across FIGS. 4C-4G, several observations can be made about the first layer 164 containing starch and calcium carbonate:
(i) the layer 164 is not continuous in the direction of the base web 140;
(ii) the layer 164 does not have uniform thickness;
(iii) the layer 164 has non-uniform thickness;
(iv) the layer 164 does not have a smooth surface; and
(v) the actual thickness of the first layer 164 can be greater than the actual thickness of the second layer 166, even though the second layer is usually thicker than the first layer.
A similar examination of the second layer 166, which does not include starch, as that layer extends across FIGS. 4C-4G permits several similar observations:
(i) the second layer 166 is not continuous in the direction of the base web 140;
(ii) the second layer 166 does not have a uniform thickness;
(iii) the second layer 166 has a non-uniform thickness;
(iv) the second layer 166 tends to have a smooth surface, but the base web (paper) has areas—e.g., 170 (FIG. 4D), 172, 174 (FIG. 4E), and 176 (FIG. 4F)—which are devoid of the add-on material constituting the second layer 166.
Differences such as those discussed above demonstrate that the schematic descriptions of paper with one or more layers of add-on material are at significant variance with the real world results of applying one or more layers of add-on material to a base web 140. Accordingly, while the schematic representations of add-on layers fairly show the process application rates, and might be used as a guide to etch application zones of a gravure print cylinder or the like, those schematic representations do not accurately represent the structure of the finished wrapper prepared by applying one layer of add-on material to a base web.
An Illustrative Embodiment—Solid Band Pattern
Referring now to FIG. 2, a wrapper for a smoking article is prepared by applying a pattern 126 of add-on material to a base web 140. The add-on material preferably comprises an aqueous starch solution having a starch in the range of about 25% to about 35% by weight. In addition, the add-on material preferably includes chalk (i.e., calcium carbonate) in the range of about 60% to about 80% as well as an anti-wrinkling agent in the range of about 10% to about 20%, where the percentages of chalk and the anti-wrinkling agent are percentages of the weight of starch used in the aqueous solution.
In a presently preferred embodiment the add-on material is applied to the base web 140 in a substantially continuous, transversely extending, solid band 126 by a single printing step and dried to remove moisture from the add-on material. The resulting wrapper is then used to construct a smoking article 120 (see FIG. 1). The smoking article 120 typically includes a tobacco rod 122 having a wrapper 123 surrounding a quantity of cut filler tobacco 124. A suitable filter 132 may be provided at one end of the tobacco rod 122. Using wrapper as described above, the tobacco rod 122 (and thus the smoking article 120) exhibits a substantially solid banded arrangement of add-on material where the band 126 extends circumferentially around the tobacco rod 122 and has a band width (measured in the direction of the axis 134) in the range of about 6 to about 7 mm.
With inclusion of the anti-wrinkling agent, such as 1,2 propylene glycol, in this embodiment as described, one may achieve the associated advantages summarized above (in the Summary) and detailed further in the description which follows.
With inclusion of the chalk in this embodiment as described, one may abate the tendency of the banded paper cigarettes to self-extinguish, enhance appearance of the product to a consumer and achieve these and other associated advantages summarized above (in the Summary) and detailed further in the description which follows.
It is also to be appreciated that with the solid band construction as described in reference to FIG. 1 one obtains a wrapper which is capable of contributing a desirable IP performance to the smoking article i.e., no greater than 25%, and which may include in various applications, an IP performance of less than 25%.
Difficulties Encountered with Applying Aqueous, Preferably Starch, Add-On Solutions
There are advantages with the concept of using aqueous starch solutions as add-on material for making banded wrapper to control IP characteristics of smoking articles manufactured using such banded wrapper. However, the application of aqueous starch solutions to a base web creates difficulties For example, aqueous starch solutions have a tendency to penetrate the irregular, rough, and porous surface of the base web 140 (see FIG. 2), and a tendency to cause transverse shrinking of the base web in the vicinity of the banded regions. As to the last point, it has been observed that when applying an aqueous starch solution to a base web about 36 inch in transverse dimension, the web may shrink about from 0.50 inch to 0.75 inch or more upon drying. This degree of shrinking would frustrate maintaining proper registration through printing and other conversion operations.
Since shrinkage is localized to the banded regions, the transverse width of the base web in the space between adjacent banded regions is greater than the transverse width of the base web in the banded regions. That disparity in transverse width gives rise to transverse waviness in the base web in those spaces between banded regions.
Such waviness in the wrapper adversely affects both the subsequent handling of the wrapper and the manufacture of smoking articles from the wrapper. For example, when wrapper with waviness is wound on a spool, or slit and wound on bobbins, the winding process flattens the waviness causing creases in the wrapper. When the creased wrapper is used to manufacture smoking articles, those creases in the wrapper are carried into the smoking articles resulting in visually unacceptable smoking articles.
Anti-Wrinkling Agent
The inclusion of an anti-wrinkling agent (preferably, such a propylene glycol) in an aqueous starch solution used to make banded wrapper in a manner consistent with the teaching herein can reduce transverse shrinkage to operationally manageable levels, alleviate pronounced wrinkling and essentially eliminate creasing problems that first presented themselves. Inclusion of an anti-wrinkling agent has been found to have additional benefits, too. For example, when an anti-wrinkling agent is incorporated into the aqueous starch solution, the anti-wrinkling agent functions as a plasticizer so that the starch is more elastic during the drying process and in the finished paper. Cracking and flaking at banded regions was alleviated. In addition, the presence of the anti-wrinkling agent appears to cause the starch solution to reside more on the surface of the base web with less penetration into that material, and thus enhance film formation. Shrinkage of the wrapper in the vicinity of banded regions formed from an aqueous starch solution that includes an anti-wrinkling agent has been observed to be in the range of about 0.0625 to 0.125 inch for a 36 inch wide base web—a range which does not result in creasing or excessive waviness. Further, inclusion of an anti-wrinkling agent in the aqueous starch solution has been found to make possible the application of add-on material to be applied to the base web in a single application, printing pass, or the like, provided that sufficient drying capability is established with such practices. Moreover, the inclusion of an anti-wrinkling agent in the aqueous starch solution to be applied in patterns may exhibit more intricacy than solid band regions, because print registration can be more precisely maintained if multiple print stations are used. In addition, the pot life of the aqueous starch solution is materially improved by the inclusion of an anti-wrinkling agent as disclosed herein.
The foregoing advantages will be better understood by those skilled in the art from the following teachings. Referring now to FIG. 2, the regions 126 of add-on material determine and regulate the IP and SE characteristics of the smoking article. Those regions 126 of add-on material are applied to a base web 140 (see FIG. 2) of the wrapper 123 and then formed into a tobacco rod in conventional cigarette making equipment. Nominal permeability of the base web 140 may be in the range of about 25 to about 100 CORESTA. Currently, the preferred nominal permeability of the base web lies in the range of about 33 to about 65 CORESTA, with the most preferred nominal permeabilities being about 33 and about 60. The base web 140 has a longitudinal direction 142 extending along the length of the wrapper 123 and a transverse direction 144 extending transversely across of the wrapper 123 so as to be generally perpendicular or transverse to the longitudinal direction 142.
Those regions 126 of add-on material may be applied to the base web 140 preferably by a printing technique. While one or more printing technique (selected from the group consisting of direct printing, offset printing, inkjet printing, gravure printing, and the like) may be used to apply the region 126, preferably a gravure printing process will be used. Gravure printing provides ample control over deposition rates, deposition patterns, and the like, and is suitable for high-speed printing on the base web 140. For purposes of this disclosure, “high-speed” printing refers to printing processes where the base web 140 advances through the printing process at a linear speed greater than about 300 feet/min. For cigarette manufacturing purposes, base web printing speeds greater than 450 feet/min. are preferred, and speeds greater than 500 feet/minute or more are even more preferred. In this regard, the rates of deposition for add-on material, as well as the quality of the pattern of deposited add-on material, can vary considerably when wrapper prepared by high-speed printing processes is compared with wrapper prepared by low-speed printing processes. Higher-speed printing operations can achieve both desirable IP values (performance) and desired SE values (performance).
Remarkably, it has been found that a base web may be converted (printed) to include bands in accordance with the embodiment described with reference to FIG. 7 at 1000 feet per minute, with acceptable paper appearance (i.e., without quality defects) and without elevated or unacceptable statistical occurrences of creases or wrinkles.
One object of this description is to provide wrappers 123 (see FIG. 2) produced at commercial-scale high-speed which, when formed into a tobacco rod, exhibit IP values no greater than 25%. Accordingly, deposit rates and characteristics of the resulting printed regions are important features of high-speed printing here. While that IP value is considered to be adequate at this time, even more preferred is an IP value for the resulting smoking article no greater than about 15%; and the most preferred IP value for the resulting smoking article is no greater than about 10%. Lower SE values are also desired. In this connection, while an SE value no greater than 50% is desirable, a more preferred SE value is less than about 25%; and the most preferred SE value is less than about 10%.
The materials used for the regions of add-on material can be important in the IP and SE performance of a smoking article manufactured using the wrapper discussed herein. In one embodiment, the regions of add-on material may be printed with a solution comprising a mixture of calcium carbonate (or chalk) particles, starch, and an anti-wrinkling agent. As with the starch and anti-wrinkling agent solution, the solution comprising a mixture of calcium carbonate (or chalk) particles, starch, and an anti-wrinkling agent preferably is applied as an aqueous solution, but a non-aqueous solution also falls within the spirit and scope of this disclosure.
This disclosure contemplates that various anti-wrinkling agents are suitable to attain the desired characteristics described herein. For example, the anti-wrinkling agent can be selected from the group consisting of glycerin, 1,2 propylene glycol, propylene glycol, and the like. In particular, the anti-wrinkling agent propylene glycol is most preferred.
Generally speaking, this disclosure contemplates that a combination of anti-wrinkling agent and calcium carbonate will be added to a nominal aqueous starch solution to obtain the add-on solution to be used for printing. For the nominal aqueous starch solutions used in this description, the starch may comprise from about 25% to about 35%, by weight, of the nominal solution. Preferably, the starch may comprise from about 28% to about 32%, by weight of the nominal solution. Most preferably, starch may comprise about 30%, by weight, of the nominal solution.
An anti-wrinkling agent is preferably added to the nominal starch solution, with the weight of the anti-wrinkling agent being in the range of about 10% of the weight of the starch in the nominal starch solution to an upper value established by the capacity of drying equipment to adequately dry the propylene-glycol containing solution. Quantitatively, that upper value is about 20% for conventional gravure printing apparatus. Preferably, the weight of the anti-wrinkling agent will be in the range of about 20% to about 30%. Most preferably, the weight of the anti-wrinkling agent will be about 25% of the weight of the starch in the nominal starch solution.